Low temperature thermochronology plays a key role in the study of the tectonic evolution of the upper crust.History modeling of apatite fission-track requires the apparent age and the confined track-length distributio...Low temperature thermochronology plays a key role in the study of the tectonic evolution of the upper crust.History modeling of apatite fission-track requires the apparent age and the confined track-length distribution of spontaneous tracks.Obtaining length data does not require either thermal neutron irradiation or LA-ICP-MS measurements of the uranium content of the grains.This paper attempts to decouple the apatite fission-track age from the apatite fission-track length,but to combine the fission-track lengths with the respective apatite U-Th/He age to model the thermal history.The experiments were designed and conducted using a new Mathematica®modeling software“Low-T Thermo”.Results of this modeling show that the thermal history modeling of apatite U-Th/He and fission-track ages can constrain the apatite fission-track length thermal history in the He partial retention zone and fission-track partial annealing zone,respectively.It implies that this combination of apatite fissiontrack length and apatite U-Th/He age has not been implemented before but is presented here as an alternative way of determining thermal histories without the addition of apatite fission-track age.展开更多
By means of the vitrinite reflectance and U-Th/He dating of apatite and zircon in cut- ting samples from the T3x-K1j formations in the Yuanba （元坝） area of Northeast Sichuan （四川） Basin, a correlation has been e...By means of the vitrinite reflectance and U-Th/He dating of apatite and zircon in cut- ting samples from the T3x-K1j formations in the Yuanba （元坝） area of Northeast Sichuan （四川） Basin, a correlation has been established between the He-derived age and depth/temperature in this area assuming helium closure temperature of apatite in this area being 95 ℃. Mesozoic strata （T3x-Kd＇） experienced helium closure temperature of apatite approaching 95 ℃, but didn＇t reach the helium closure temperature of zircon （ca. 170-190 ℃） although some reached the highest pa- laeogeothermal temperature of about 170 ℃. The Mesozoic strata in the Yuanba area experienced an important uplift and denudation during Paleogene-Neogene periods （0.2-36.4 Ma）, the erosion rate being about 109.9 m/Ma. The K1] Formation and overlying strata experienced a maximum de- nudation loss of about 4 000 m. Geotemperatures gradually fell to the helium closure temperature of apatite and then fell further to the current temperature. The thermal evolution history of this area indicates that the maximum palaeogeothermal temperature of Mesozoic strata was close to 170- 190 ℃, prior to the strata being uplifted. During the period between 176 and 36 Ma, the palaeogeo- thermal temperature fell to 95-170 ℃. and after 36 Ma, it continued to fall to the present geotem- perature of less than 95 ℃.展开更多
New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,defor...New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,deformation,and sedimentation.Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval,which were deposited closely following the 1.65-1.63 Ga Mazatzal orogeny.In Baraboo Interval strata,muscovite parallel to slatey cleavage,in hydrothermal veins,in quartzite breccia,and in metamorphosed paleosol yielded ^(40)Ar/^(39)Ar plateau ages of 1493-1465 Ma.In addition,U-Th-total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488±20 Ma,and recrystallized hematite in folded metapelite gave a mean U/Th-He age of 1411±39 Ma.Post-Baraboo,arkosic polymictic conglomerate,which contains detrital zircon with a minimum peak age of 1493 Ma,was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith.This episode of magmatism,regional deformation and metamorphism,and sedimentation,which is designated herein as the Baraboo orogeny,provides a midcontinental link between the Picuris orogeny to the southwest and the Pinware orogeny to the northeast,completing the extent of early Mesoproterozoic(Calymmian)orogenesis for 5000 km along the southern margin of Laurentia.This transcontinental orogen is unique among Precambrian orogenies for its great width(-1600 km),the predominance of ferroan granites derived from partial melting of lower continental crust,and the prevalence of regional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.展开更多
Fission-track, (U-Th)/He thermochronology, and cooling properties indicate that the southern Daba arcuate zone (SDBAZ) underwent a distinctive phase of rapid cooling in 153-100 Ma at a rate of 1.44-1.90°C/Ma. Thi...Fission-track, (U-Th)/He thermochronology, and cooling properties indicate that the southern Daba arcuate zone (SDBAZ) underwent a distinctive phase of rapid cooling in 153-100 Ma at a rate of 1.44-1.90°C/Ma. This rapid uplifting strongly contrasts with (1) the previous, rapid foreland subsidence during Early to Middle Jurassic in response to late-orogenic compression from the Qinling belt, (2) the succeeding long, slow cooling phase and relative thermal stability that occurred during the 100-45 Ma period. This rapid cooling event in the SDBAZ parallels those experienced by two adjacent upheavals of Huangling (HLUZ) and Hannan-Micang (HMUZ), with cooling rates of 2.22-3.17°C/Ma for the HLUZ in 160-126 Ma, 4.91°C/Ma for the southern HMUZ in 150-125 Ma, as well as 2.11°C/Ma for the northern HMUZ in 150-105 Ma. Comparing thermal histories among the SDBAZ, the HLUZ, the HMUZ, and the Wudang metamorphic zone (WDMZ), we infer that the Daba arcuate structural belt formed in 153-100 Ma. The combined dating data support a correlation with a low-angle arcuate south-thrusting of the Qinling orogen triggered by northward convergence of the Yangtze Craton, contemporaneously encountering rigid basement obstructions from the HLUZ and the HMUZ, respectively. Both the SDBAZ and neighboring domains additionally underwent a comparatively fast cooling and uplift since about 45 Ma.展开更多
The thermal evolution of source rocks in the Paleozoic stratigraphic sequences has been an outstanding problem for petroleum exploration in the Tarim Basin, as the thermal history of the Paleozoic could not be reconst...The thermal evolution of source rocks in the Paleozoic stratigraphic sequences has been an outstanding problem for petroleum exploration in the Tarim Basin, as the thermal history of the Paleozoic could not be reconstructed objectively due to the lack of effective thermal indicators in the early Paleozoic carbonate successions. The (U-Th)/He thermochronometry of apatite and zircon has recently been used as an effective tool to study the structural uplift and thermal history of sedimentary basins. The Paleozoic tectonothermal histories of two typical wells in the Tarim Basin were modeled using the thermal indicators of (U-Th)/He, apatite fission track (AFT), and vitrinite reflectance (Ro) data in this paper. The Paleozoic strata in the two wells were shallow due to persistent uplift and significant erosion during the Hercynian tectonic events (from Devonian to Triassic). Therefore, the paleothermal indicators in the Paleozoic strata may retain the original thermal evolution and can be used to re- construct the Paleozoic thermal history of the Tarim Basin. The apatite and zircon helium ages from core and cuttings samples were analyzed and the Paleozoic thermal histories of wells KQ1 and T1 were modeled by combining helium ages, AFT, and equivalence vitrinite reflectance (VRo) data. The modeling results show that the geothermal gradient evolution is different in the Kongquehe Slop and Bachu Uplift of Tarim Basin during the Paleozoic. The thermal gradient in Well T1 on the Bachu Up- lift was only 28–30°C/km in Cambrian, and it increased to 30–33°C/km in Ordovician and 31–34°C/km during the Silurian and Devonian. The thermal gradient of Ordovician in Well KQ1 on the Kongquehe Slope was 35°C/km and decreased to 32–35°C/km during the Silurian and Devonian. Therefore, the combined use of (U-Th)/He ages and other thermal indicators appears to be useful in reconstructing the basin thermal history and provides new insight into the understanding of the early Paleozoic thermal history of the Tarim Basin.展开更多
基金supported by the National Natural Science Foundation of China(Nos.42072229,41102131)the Fundamental Research Fund for the Central Universities of China(No.12lgpy22)+2 种基金the Guangdong Natural Science Foundation(No.2021A1515011658)the Science and Technology Program of Guangzhou(No.202002030184)the China Scholarship Council。
文摘Low temperature thermochronology plays a key role in the study of the tectonic evolution of the upper crust.History modeling of apatite fission-track requires the apparent age and the confined track-length distribution of spontaneous tracks.Obtaining length data does not require either thermal neutron irradiation or LA-ICP-MS measurements of the uranium content of the grains.This paper attempts to decouple the apatite fission-track age from the apatite fission-track length,but to combine the fission-track lengths with the respective apatite U-Th/He age to model the thermal history.The experiments were designed and conducted using a new Mathematica®modeling software“Low-T Thermo”.Results of this modeling show that the thermal history modeling of apatite U-Th/He and fission-track ages can constrain the apatite fission-track length thermal history in the He partial retention zone and fission-track partial annealing zone,respectively.It implies that this combination of apatite fissiontrack length and apatite U-Th/He age has not been implemented before but is presented here as an alternative way of determining thermal histories without the addition of apatite fission-track age.
基金supported by the National Basic Research Program of China(No.2012CB214801)China Petroleum and Chemical Corporation Program(No.P120009)
文摘By means of the vitrinite reflectance and U-Th/He dating of apatite and zircon in cut- ting samples from the T3x-K1j formations in the Yuanba （元坝） area of Northeast Sichuan （四川） Basin, a correlation has been established between the He-derived age and depth/temperature in this area assuming helium closure temperature of apatite in this area being 95 ℃. Mesozoic strata （T3x-Kd＇） experienced helium closure temperature of apatite approaching 95 ℃, but didn＇t reach the helium closure temperature of zircon （ca. 170-190 ℃） although some reached the highest pa- laeogeothermal temperature of about 170 ℃. The Mesozoic strata in the Yuanba area experienced an important uplift and denudation during Paleogene-Neogene periods （0.2-36.4 Ma）, the erosion rate being about 109.9 m/Ma. The K1] Formation and overlying strata experienced a maximum de- nudation loss of about 4 000 m. Geotemperatures gradually fell to the helium closure temperature of apatite and then fell further to the current temperature. The thermal evolution history of this area indicates that the maximum palaeogeothermal temperature of Mesozoic strata was close to 170- 190 ℃, prior to the strata being uplifted. During the period between 176 and 36 Ma, the palaeogeo- thermal temperature fell to 95-170 ℃. and after 36 Ma, it continued to fall to the present geotem- perature of less than 95 ℃.
基金Detrital zircon analyses were funded in part by the USGS National Cooperative Geologic Mapping Program under award G16AC00143(2016)to EKS.Support for the Arizona LaserChron Center,where detrital zircon analyses of samples 07ES15 and 05ES15 were performed,was provided by NSFEAR 1649254.Support for monazite geochronology was partially provided by an Institute for Lake Superior Geology student research grant and NSF-EAR 0620101 to AVL.
文摘New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476-1470 Ma Wolf River granitic batholith was not an isolated igneous event,but was accompanied by regional metamorphism,deformation,and sedimentation.Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval,which were deposited closely following the 1.65-1.63 Ga Mazatzal orogeny.In Baraboo Interval strata,muscovite parallel to slatey cleavage,in hydrothermal veins,in quartzite breccia,and in metamorphosed paleosol yielded ^(40)Ar/^(39)Ar plateau ages of 1493-1465 Ma.In addition,U-Th-total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488±20 Ma,and recrystallized hematite in folded metapelite gave a mean U/Th-He age of 1411±39 Ma.Post-Baraboo,arkosic polymictic conglomerate,which contains detrital zircon with a minimum peak age of 1493 Ma,was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith.This episode of magmatism,regional deformation and metamorphism,and sedimentation,which is designated herein as the Baraboo orogeny,provides a midcontinental link between the Picuris orogeny to the southwest and the Pinware orogeny to the northeast,completing the extent of early Mesoproterozoic(Calymmian)orogenesis for 5000 km along the southern margin of Laurentia.This transcontinental orogen is unique among Precambrian orogenies for its great width(-1600 km),the predominance of ferroan granites derived from partial melting of lower continental crust,and the prevalence of regional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.
基金supported by National Natural Science Foundation of China (Grant No.40872138)Science and Technology Research Key Project of Ministry of Education (Grant No.107042)Excellent Academic Leaders Program of Shanghai (Grant No.08XD14042)
文摘Fission-track, (U-Th)/He thermochronology, and cooling properties indicate that the southern Daba arcuate zone (SDBAZ) underwent a distinctive phase of rapid cooling in 153-100 Ma at a rate of 1.44-1.90°C/Ma. This rapid uplifting strongly contrasts with (1) the previous, rapid foreland subsidence during Early to Middle Jurassic in response to late-orogenic compression from the Qinling belt, (2) the succeeding long, slow cooling phase and relative thermal stability that occurred during the 100-45 Ma period. This rapid cooling event in the SDBAZ parallels those experienced by two adjacent upheavals of Huangling (HLUZ) and Hannan-Micang (HMUZ), with cooling rates of 2.22-3.17°C/Ma for the HLUZ in 160-126 Ma, 4.91°C/Ma for the southern HMUZ in 150-125 Ma, as well as 2.11°C/Ma for the northern HMUZ in 150-105 Ma. Comparing thermal histories among the SDBAZ, the HLUZ, the HMUZ, and the Wudang metamorphic zone (WDMZ), we infer that the Daba arcuate structural belt formed in 153-100 Ma. The combined dating data support a correlation with a low-angle arcuate south-thrusting of the Qinling orogen triggered by northward convergence of the Yangtze Craton, contemporaneously encountering rigid basement obstructions from the HLUZ and the HMUZ, respectively. Both the SDBAZ and neighboring domains additionally underwent a comparatively fast cooling and uplift since about 45 Ma.
基金supported by Key Project of Ministry of Education of China (Grant No. 308005)National Basic Research Program of China (Grant No. 2005CB422102)State Key Laboratory of Petroleum Resource and Prospecting (Grant No. PRPJC2008-01)
文摘The thermal evolution of source rocks in the Paleozoic stratigraphic sequences has been an outstanding problem for petroleum exploration in the Tarim Basin, as the thermal history of the Paleozoic could not be reconstructed objectively due to the lack of effective thermal indicators in the early Paleozoic carbonate successions. The (U-Th)/He thermochronometry of apatite and zircon has recently been used as an effective tool to study the structural uplift and thermal history of sedimentary basins. The Paleozoic tectonothermal histories of two typical wells in the Tarim Basin were modeled using the thermal indicators of (U-Th)/He, apatite fission track (AFT), and vitrinite reflectance (Ro) data in this paper. The Paleozoic strata in the two wells were shallow due to persistent uplift and significant erosion during the Hercynian tectonic events (from Devonian to Triassic). Therefore, the paleothermal indicators in the Paleozoic strata may retain the original thermal evolution and can be used to re- construct the Paleozoic thermal history of the Tarim Basin. The apatite and zircon helium ages from core and cuttings samples were analyzed and the Paleozoic thermal histories of wells KQ1 and T1 were modeled by combining helium ages, AFT, and equivalence vitrinite reflectance (VRo) data. The modeling results show that the geothermal gradient evolution is different in the Kongquehe Slop and Bachu Uplift of Tarim Basin during the Paleozoic. The thermal gradient in Well T1 on the Bachu Up- lift was only 28–30°C/km in Cambrian, and it increased to 30–33°C/km in Ordovician and 31–34°C/km during the Silurian and Devonian. The thermal gradient of Ordovician in Well KQ1 on the Kongquehe Slope was 35°C/km and decreased to 32–35°C/km during the Silurian and Devonian. Therefore, the combined use of (U-Th)/He ages and other thermal indicators appears to be useful in reconstructing the basin thermal history and provides new insight into the understanding of the early Paleozoic thermal history of the Tarim Basin.
